1. Field of the Invention
The present invention relates generally to a header tube for heat exchangers. More specifically, the invention relates to header tubes that are strengthened by using stampings on each side of webs formed in the tubes and flattening the webs so that the cross-section of the tube has a D-shaped profile.
2. Related Art
In known types of header tubes, the stability of the webs in the transition to the cylindrical surface of the tube is achieved in some designs by lightly pressing down the middle of the webs at their highest point, until they are more or less flat or have a concave shape toward the inside of the tube. However, the change of direction of the surface toward the inside of the tube only results in a change of the slope of the transition to the cylindrical surface of the tube.
Other designs have transverse separating walls within the tube which are perpendicular to the tube axis, whereby each transverse wall radially supports one of the webs. The installation of the transverse walls to stabilize and hold the webs results in additional time and cost factors.
Another type of header tube is described in European Patent Document EP 0 198 581 81, which concerns a heat exchanger with header tubes that are spaced apart and largely parallel to each other. Each of the header tubes has spaced holes in the shape of slots which are perpendicular to the tube axis and separated by webs of metal.
The slots in the tube segment of one of the header tubes are arranged to be directly opposite corresponding slots in the other header tube. Hollow, flat pipes are installed between the header tubes and inserted in the associated slots, to be rigidly attached to the slots by soldering the contact surfaces such as by soldering. Each of the webs is convex, both across the header tube and also along the direction of the tube axis, having a largely curved surface, i.e., the parts of the tube segment between the slots are shaped as a dome.
In order to improve the poor strength of the curved webs of metal in their transition to the cylindrical surface of the tube, the edges of the slots, which are parallel to the flat pipes are folded over perpendicular to the tube axis. Shaping the slots in this way represents an additional time and cost factor during manufacture.
When the heat transfer fluid flows through the heat exchanger, this can result in pressure fluctuations which are transferred to the domed webs as vibration or shock waves, which can endanger poorly soldered connections between the flat pipes and the header tubes.